Impaired Loans and Valuation Allowance for Loan Losses - Company's Recorded Investments in Impaired Loans and the Related Valuation Allowances (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded Investment, Total	$ 52,969,000	$ 82,901,000
Unpaid Principal Balance, Total	62,446,000	93,023,000
Related Valuation Allowance, Total	5,446,000	7,269,000
Average Recorded Investment, Total	66,603,000	96,439,000	119,528,000
Interest Income Recognized, Total	1,260,000	3,054,000	3,541,000
Construction and Land Development [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance, Recorded Investment	2,561,000	1,128,000
Recorded Investment, Total	3,681,000	4,025,000
With no related allowance, Unpaid Principal Balance	3,180,000	1,608,000
Unpaid Principal Balance, Total	4,377,000	4,549,000
With no related allowance, Related Valuation Allowance	0	0
With no related allowance, Average Recorded Investment	2,446,000	1,399,000
With no related allowance, Interest Income Recognized	102,000	5,000
With related allowance, Recorded Investment	1,120,000	2,897,000
With related allowance, Unpaid Principal Balance	1,197,000	2,941,000
Related Valuation Allowance, Total	149,000	230,000
With related allowance, Average Recorded Investment	1,347,000	3,539,000
Average Recorded Investment, Total	3,793,000	4,938,000
With related allowance, Interest Income Recognized	36,000	127,000
Interest Income Recognized, Total	138,000	132,000
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance, Recorded Investment	4,481,000	12,357,000
Recorded Investment, Total	12,418,000	38,487,000
With no related allowance, Unpaid Principal Balance	6,577,000	14,337,000
Unpaid Principal Balance, Total	14,623,000	40,985,000
With no related allowance, Related Valuation Allowance	0	0
With no related allowance, Average Recorded Investment	7,382,000	12,103,000
With no related allowance, Interest Income Recognized	28,000	433,000
With related allowance, Recorded Investment	7,937,000	26,130,000
With related allowance, Unpaid Principal Balance	8,046,000	26,648,000
Related Valuation Allowance, Total	638,000	2,264,000
With related allowance, Average Recorded Investment	17,264,000	39,527,000
Average Recorded Investment, Total	24,646,000	51,630,000
With related allowance, Interest Income Recognized	395,000	1,304,000
Interest Income Recognized, Total	423,000	1,737,000
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance, Recorded Investment	12,366,000	15,463,000
Recorded Investment, Total	35,731,000	39,719,000
With no related allowance, Unpaid Principal Balance	17,372,000	22,022,000
Unpaid Principal Balance, Total	42,138,000	46,774,000
With no related allowance, Related Valuation Allowance	0	0
With no related allowance, Average Recorded Investment	14,512,000	12,019,000
With no related allowance, Interest Income Recognized	81,000	455,000
With related allowance, Recorded Investment	23,365,000	24,256,000
With related allowance, Unpaid Principal Balance	24,766,000	24,752,000
Related Valuation Allowance, Total	4,528,000	4,700,000
With related allowance, Average Recorded Investment	22,899,000	26,795,000
Average Recorded Investment, Total	37,411,000	38,814,000
With related allowance, Interest Income Recognized	566,000	696,000
Interest Income Recognized, Total	647,000	1,151,000
Commercial and Financial [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance, Recorded Investment	153,000	0
Recorded Investment, Total	166,000	0
With no related allowance, Unpaid Principal Balance	153,000	0
Unpaid Principal Balance, Total	166,000	0
With no related allowance, Related Valuation Allowance	0	0
With no related allowance, Average Recorded Investment	19,000	7,000
With no related allowance, Interest Income Recognized	9,000	0
With related allowance, Recorded Investment	13,000	0
With related allowance, Unpaid Principal Balance	13,000	0
Related Valuation Allowance, Total	13,000	0
With related allowance, Average Recorded Investment	1,000	34,000
Average Recorded Investment, Total	20,000	41,000
With related allowance, Interest Income Recognized	1,000	0
Interest Income Recognized, Total	10,000	0
Consumer [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance, Recorded Investment	425,000	223,000
Recorded Investment, Total	973,000	670,000
With no related allowance, Unpaid Principal Balance	569,000	255,000
Unpaid Principal Balance, Total	1,142,000	715,000
With no related allowance, Related Valuation Allowance	0	0
With no related allowance, Average Recorded Investment	162,000	431,000
With no related allowance, Interest Income Recognized	19,000	12,000
With related allowance, Recorded Investment	548,000	447,000
With related allowance, Unpaid Principal Balance	573,000	460,000
Related Valuation Allowance, Total	118,000	75,000
With related allowance, Average Recorded Investment	571,000	585,000
Average Recorded Investment, Total	733,000	1,016,000
With related allowance, Interest Income Recognized	23,000	22,000
Interest Income Recognized, Total	$ 42,000	$ 34,000